Breed does make a difference. They will lay between 18-24 weeks generally. When they start doing the egg squat they'll be close. My BR started laying at 19 weeks and my Delaware and JG are 21 weeks and no eggs yet.

Pullets start laying usually around 5-7 months. Though my barred rock layed at 4 months, and my cuckoo marans started laying at 8 months. I all depends on the hen. Her face will start to turn red and my buttercup pullet started to act curious about the nesting boxes and she was getting in and out.....sure enough she layed an egg at about 6 months.